Rapise 1.5

You can use the special SeSFindObj('object name') command to perform the check:

if(SeSFindObj('Object Name'))
{
    // Object is available
}
else
{
    // Object is not available 
}

 Rapise 7.0+

If you have a web test then you may use Navigator.CheckObjectExists that also accepts XPath as a parameter.

Also in desktop, mobile and web tests one may use Global.DoWaitFor with timeout parameter set to 1.